Method for localization and generation of short critical sequence

ABSTRACT

A method for localization and generation of short critical sequence uses an automatic test equipment to test an electronic device (e.g., memory device) by circuit simulation to localize and re-generate a very short critical sequence from a set of long worst-case pattern. The method includes defining a failure mechanism condition for search and localization process and re-production of the short critical sequence based on a mutation process from the critical sequence detected from a step (I) phase and number of pattern defined in population using a genetic algorithm step (II) phase.

TECHNICAL FIELD

The present invention relates generally to a system and method testing electronic devices, and more particularly to a system and method for localization and generation of short critical sequences.

BACKGROUND

Embodiments of the invention concern a method for localization and generation of short critical sequence using an automatic test equipment to test an electronic device by circuit simulation, e.g. a memory device, to localize and regenerate a very short critical sequence from a set of long worst-case pattern.

The major challenge and technical problem of the prior art is to figure out how to localize and regenerate a very short critical sequence from a set of long worst-case pattern automatically. In many situations, a set of worst-case patterns is detected and they cannot pin point the critical sequence directly via circuit-level simulation.

It is simply that the pattern sequence will take a very long time to run simulation. For example, 200 pattern cycles can take approximately five days for simulation of a device. In addition, it is very difficult to analyze the failure based a few thousand cycles sequence. Since not every sequence uncovers the problem, it is difficult to determine the critical issues. Ultimately, it is necessary to narrow down this sequence into a very small sequence, which can pinpoint the problem directly.

Usually, this set of long worst-case test patterns can either be detected by a random approach or an optimization (neural network and generic algorithm as proposed before) approach, which can guarantee at least equal or better worst-case sequence than the original long pattern, then it can be used to address the problem accurately in ATE (automatic test equipment) analysis phase as well as circuit simulation phase.

The typical way of dealing with this problem is very inefficient or is just trial and error manually for different smaller pieces of pattern sequence. Even so, it will either take a long time to extract this short sequence with less worst-case possibilities or cannot detect the same failure mechanism at all. It was found that a situation that a failure occurs at completely different locations; one is needed to provoke another. In order to obtain the full effect of the failure, the methodology must be able to determine both cause and effect sequence.

Thus if one tries to cut the pattern into many small pieces in a systematic way (it is what could tried manually at most, otherwise one can just figure it out now, there are an unbelievable number of combinations), then one will never find the short critical sequence to provoke the similar failure again. There exist no tool or standard technique yet.

In the following are listed some practical technical problems of extracting a short critical sequence from a set of long pattern, which are the disadvantages under the prior art. In one case, one could manually cut the pattern into many smaller pieces systematically and then try them one by one. In any event, simply taking a long time cannot guarantee the extraction is accurate.

If a failure is provoked by several random vector locations, one must be provoked by another to generate the full effect of the failure. Then the typical systematic way will either fail to detect this sequence or a very large effort (time) with a very experienced engineer can detect this.

A typical way of narrowing down the pattern cannot determine cause and effect sequence automatically and efficiently. A very short sequence must be obtained for circuit-level simulation and detail analysis at ATE. The typically used method cannot be guaranteed to have a very short sequence. In some cases, the manual process can cut the pattern down from million of vector cycles to hundred cycles.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides an accurate and fast localization of the short sequence instead of manual work. Embodiments of the invention can generate an at least equal or better worst-case short sequence. Further, embodiments of the invention can handle the localization and generation of short critical sequence efficiently and automatically.

The preferred embodiment of the invention is based on two different steps. The first step is search and localize the sequence (cause and effect) and the second step is further optimization the detected short sequence and generate another set of short sequence with guarantee at least equal or better worst-case than original sequence. The combination of the first and the second step creates the very first automatic extraction short sequence concept using evolution technique (e.g. generic algorithm).

A major advantage of the invention is that this technique provides an accurate and fast localization of the short sequence instead of manual work. Furthermore, guarantee at least equal or better worst-case short sequence is generated using evolution technique, while typical or prior art cannot handle this problem efficiently and automatically.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows experimental results using 5000 worst-case pattern sequence (Y-axis: VDD Power Supply (V), X-axis: TRC Memory Read Cycles (ns));

FIG. 2 shows two sub-steps of the first step;

FIG. 3 shows the third sub-step of the first step with the final compression solution of the short sequence via bound and search technique; the final short sequence satisfying all failure mechanism condition; and

FIG. 4 shows the completed method of genetic linear and optimization technique.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.

In the step (I) phase it is necessary to define the failure mechanism condition for search and localization process. The condition can be a single point or multiple points. It depends on how the failure effect is described and usually it can be easily referred to the shmoo plot analysis based on long worst-case pattern sequence. For example, as FIG. 1 shows the failure using 5000 vector cycles—long pattern provokes a high VDD malfunction at 2,09 V when refresh-oscillator is free running.

The failure mechanism condition is then described by three multiple conditions as shown in FIG. 1. It is also possible to define more condition points in order to describe the failure effect as accurate as possible.

Next it is necessary to define the number of cycles for the short sequence. For example there are defined 10 cycles; the search process begins with linearly increase with 10 cycles sequence each (i.e. divided the long pattern into every 10 cycles sequence) and test them with respect to the failure mechanism conditions. The search process will stop until the short sequence satisfying the failure mechanism conditions since the failure and reference sequence is reached and this means also that all pattern cycles or sequence after this reference point can be ignored.

In the second search phase (I) is to find out the cause and effect. The reference sequence shows the effect, and the cause must be referred to number of read in the reference sequence; and track back where the write sequence performs (cause).

All write sequences are then extracted to combine with short sequences, and test with the failure mechanism condition. If it does not satisfy the condition, then all write sequences will be extended with additional cycles referring to the before and after vector cycles within each write sequence.

The process is repeated until the condition is satisfied again. Finally, a short sequence is extracted, but likely larger than 10 cycles are defined, as the combinations are based on the appending the short 10 cycles sequence. The final step (I) phase is to compress a sequence to 10 cycles again. Thus, the algorithm will first determine all don't care vectors and dummy write vectors (since all read refer to this write is already cur always based on the failure end reference sequence, then try to throw them out and test them with respect to the failure mechanism conditions one by one (bound and search technique) until 10 cycles (a little more than 10 cycles) and mechanism conditions are satisfied.

The step (I) phase can be described in three sub-steps, see also FIGS. 2 and 3:

-   -   1.1 Find the failure end reference sequence (the effect).     -   1.2 Find the cause of the effect by tracing back process (the         cause and the effect).     -   1.3 Final compression solution of the short sequence via bound         and search technique;         this is the final short sequence satisfying all failure         mechanism conditions.

In the step (II) phase (optimization), the re-production of the short critical sequence is based on mutation process from the critical sequence detected from step (I) and number of pattern defined in population using genetic algorithm. The mutation process alters the information for each different signal groups in complete random way (e.g. address bus, command bus and data bus; this is an example of a memory device). At this way it is possible to study if the impact of the effect is based on which groups of signal changes.

The population is the collection of all the possible and potential critical short sequences in the pending case. The population will contain at least one original critical sequence detected from step (I) and combine with different mutation sequence, then start the evolution optimization process. For example, if each population contains 10 patterns, then the re-production will create another 9 short sequences by mutation process and keep one original sequence (in order to avoid loss of the originality of the critical sequence).

The optimization objective function is defined by analysis objective from the failure mechanism; as previous example shows that worst case failure mechanism is that lower the VDD failure, the better the short critical sequence. Thus, VDD failure is the objective function with respect to the different critical short sequence. For each critical short sequence, VDD will be search from 1.5 V to 2.2 V using characterization search (e.g. successive approximation which can detect even if the device parameters shift), and to determine VDD failure point.

The objective in this specific example is to detect a critical short sequence, which can cause VDD failure occurs earlier (VDD<2.09 V). This way can certainly guarantee to generate a new set of very short critical sequences with at least equal or better worst-case pattern. Therefore, the objective function (fitness in GA—Genetic Algorithm) is defined such that the analysis of the worst-case failure mechanism is the function of different short critical sequences as equation [1] shows below.

Optimization: Worst Case Failure Mechanism (Short Critical Sequence)  [1]

→Worst-case failure mechanism measured by characterization search method.

→Optimization using Genetic Algorithm (GA).

The step (II) phase has the following sub-steps:

-   2.1 Defined analysis objective of failure mechanism for fitness in     GA process -   2.2 Defined number of potential solutions in each GA population -   2.3 Pattern mutation based on critical pattern sequence from step     (I) -   2.4 Combination of all mutation pattern and original critical     pattern from step (I) -   2.5 Start optimization, fitness is detected by characterization     search technique -   2.6 The process is repeated until the optimal solution found or     maximum GA loop.

The complete method of genetic linear search and optimization technique is shown at FIG. 4.

The complete description of a method for localization and generation of short critical sequence using an automatic test equipment to test an electronic device is to find below:

-   1. Input a set of worst-case pattern. -   2. Define the failure mechanism condition for search process. -   3. Start search and localization process with respect to the failure     mechanism conditions using long worst-case pattern. -   4. Find the failure end reference sequence (effect) -   5. Find the cause of the effect by tracking back process (cause and     effect). -   6. Final compression solution of the short sequence via bound and     search technique (final short sequence satisfying all failure     mechanism conditions. -   7. Repeating steps 4 to 6 until the end of search loop. -   8. A short critical pattern sequence detected for the single     worst-case pattern. -   9. Start GA optimization using short critical pattern sequence from     step 7. -   10. Defined number of potential solutions in each GA population. -   11. Defined number of potential solutions in each GA population. -   12. Pattern mutation based on critical pattern sequence from step 7. -   13. Combination of all mutation pattern and original critical     pattern from step 7. -   14. Start optimization, until fitness is detected by     characterization search technique. -   15. Repeating step 13 and 14 until end of GA optimization loop. -   16. A set of better or equal critical pattern sequences generated     for the single long worst-case pattern. -   17. Repeating step 1 to 16 until end of long worst-case pattern. -   18. Detail ATE analysis or circuit-level simulation based on very     short critical pattern sequences.

A practical example will now be described. A design robustness analysis for a P14 PRAM memory with cold temperature hang up sequence detected after only 10 vector cycles. While typical march pattern or random pattern (20K vector cycles) via random approach cannot detected this problem at all.

The experimental results show 10 cycles pattern vs. 20K, 40K, 5000 and 1000 pattern, surprisingly 10 cycles pattern show much better worst case than any one of the above pattern sequence.

A set of worst-case input signal toggling patterns are first generated based on previous proposal (NNGA). Two patterns are detected device hang up problem at cold temperature. The pattern 1 is 5000 cycles as shown actually in FIG. 1, shows the hang up occurs above VDD=2.09 V. The pattern 2 is 1000 cycles, shows the hang up occurs as VDD=2.04 V. Unfortunately, both patterns are too large for direct circuit-level (full-chip) simulation or very detail analysis on ATE. This is how the invention becomes really useful during design analysis phase. Pattern 1 and Pattern 2 have been used to generate a set of very short worst-case sequences (10 cycles only).

While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments. 

1. A method for localization and generation of short critical sequence using an automatic test equipment to test an electronic device by circuit simulation to localize and re-generate a very short critical sequence from a set of long worst case pattern, the method comprising defining a failure mechanism condition for search and localization process and re-production of the short critical sequence based on a mutation process from the critical sequence detected from a step (I) phase and number of pattern defined in population using a genetic algorithm step (II) phase.
 2. A method according claim 1 at which the failure mechanism condition is defined as a single point or as multiple points.
 3. A method according claim 2 and comprising the step of defining a worst-case pattern sequence.
 4. A method according claim 1 at which the mutation process alters the information for each different signal groups in complete random way.
 5. A method according to claim 4 wherein the electronic device comprises a memory device.
 6. A method according to claim 5 wherein the mutation process alters information for signal groups derived from an address bus, a command bus and a data bus.
 7. A method according claim 1 at which the step (I) phase is defined by the sub-steps, the sub-steps comprising: find the failure end reference sequence; find the cause of the effect by tracking back process; and final compression solution of the short sequence via bound and search technique.
 8. A method according claim 1 at which the step (II) phase is defined by sub-steps, the sub-steps comprising: define analysis objective of failure mechanism for fitness in GA process; define number of potential solutions in each GA population; mutation of pattern based on critical pattern sequence from step (I), combination of all mutation pattern and original critical pattern from step (I), start optimization, fitness is detected by characterization search technique and repeating the process until the optimal solution is found or maximum GA loop.
 9. A method according to claim 1 wherein the electronic device comprises a memory device. 